Molecular Identification of Staphylococcus aureus Isolated from Soy Milk Sold in Retail Shops in Enugu Metropolis, Enugu State, Nigeria Using Gel Electrophoresis and Ncbi-Blast Analysis

Staphylococcus aureus is an important foodborne pathogen that is of major concern to public health especially when it becomes resistant to a last-line drug of choice like vancomycin. As the use of plant derived drinks such as soy milk have grown, the issue of microbial contamination and antimicrobial resistance is also of greater concern particularly in regions with little regulations. This study was done to determine the occurrence of Vancomycin-Resistant Staphylococcus aureus (VRSA) in soy milk retailed at shops in Thinker Corner, Enugu. Eight (8) samples of soy milk drinks were randomly purchased in retail outlets. The samples were cultured using on mannitol salt agar and subsequently identified using their morphological features, Gram stain and biochemical tests (catalase test and coagulase test). Antibiotic susceptibility test (AST) was done with vancomycin as the test antibiotic using well diffusion method on Mueller-Hinton agar after standardizing to 0.5 McFarland turbidity. The diameter of the zones of inhibition was measured in mm and interpreted using the EUCAST breakpoint guidelines. Of the eight S. aureus isolates tested, five (5) were resistant to vancomycin, with MIC values ranging from 60 to 30 mg/L. The result of the agarose gel electrophoresis r visualized under UV light showed strong, distinct bands in lane M2, M3, M4, which indicates successful PCR amplification of 16 S gene in these samples. The Basic Local Alignment Search Tool (BLAST) was used on the DNA sequences of the test isolates. The BLAST tree indicated similarities when the query sequence was compared to sequences found in the database. The detection of Vancomycin Resistant Staphylococcus aureus poses a possible health hazard and calls for routine surveillance and improved hygiene practices during the production and sales of the plant-based drinks.